Water flow detectors having a timer responsive to movement of a lever connected to a paddle are known. A known water flow detector uses an air bleed timer. U.S. Pat. No. 6,331,820 discloses a paddle type flow detector which relies on an air bleed timer. U.S. Pat. No. 4,782,333 discloses an air bleed timer. Both of these patents are incorporated herein by reference.
In general a water flow detector using an air bleed timer has a cam. The cam, when in a first position, maintains a switch assembly in a first state. The cam when in a second position enables the switch assembly to orient to a second state. The lever when moved to a second position enables the cam to move from the first position to the second position. The time it takes the cam to move depends upon the rate at which air is set to bleed out of an air chamber formed by a diaphragm. If the air is set to bleed out quickly, the cam will move quickly from the first to the second position. If the air is set to bleed out slowly, the cam will move slowly from the first to the second position and it will take longer for the switch to orient itself from the first to the second state.
The lever is moved from the first position to the second position by the flow of water in a riser pipe of a fire sprinkler assembly. The water causes the paddle to move from a first to a second position. If the lever is not in the second position, the cam cannot move from the first to the second position. Accordingly the switch can not orient from the first state to the second state. Whether the cam moves from the first to the second position depends on the rate of air bleed and the duration of suitable water flow. If the water flow stops before the air bleed is complete, the cam will be moved back to the first position by the lever prior to the cam moving to the second position. The switch will not orient to the second state. For instance, if the bleed duration is 50 seconds then the cam will move from the first to the second position in 50 seconds so long as the lever is maintained in the 2nd position by the water flow. If the lever is not maintained in a second position by the water flow for 50 seconds then the cam will not be able to move to the second position. The switch will not orient to the second state. Accordingly the longer the bleed time, the longer the water flow most continue for the switch to orient from the first to the second state. The shorter the bleed time the shorter amount of time the water flow most continue for the switch to orient from the first state to the second state. To ensure against false alarms from pressure fluctuations in the sprinkler system, a long bleed time can be helpful.